1. Field of the invention
The present invention relates to a fuel injection device for an internal combustion engine.
2. Description of the Related Art
The amount of fuel injected by individual fuel injectors usually differs at each injector, even if a fuel pressure and fuel injection time at each fuel injector are the same, and thus the actual amount of fuel injected differs at each cylinder of the engine. Also, the actual amount of fuel injected is changed by a long-term operation of the fuel injectors, even if the fuel pressure and the fuel injection time are constant. Accordingly, it is difficult to equalize the actual amount of fuel injected with a target amount of fuel injected, when this is calculated on the basis of an engine speed and an engine load.
To solve this problem, Japanese Unexamined Patent Publication No. 62-186034 discloses a device for controlling an amount of fuel to be injected to an internal combustion engine, wherein a discharge port of a fuel supply pump is connected to a fuel injector via a reservoir tank, a basic amount of fuel to be injected is calculated on the basis of the engine speed and the engine load, a difference in a fuel pressure before and after one fuel injection is determined on the basis of an output of a fuel pressure sensor for detecting a fuel pressure in the reservoir tank, the actual amount of fuel to be injected is calculated on the basis of the difference in the fuel pressure, and the basic amount of fuel to be injected is corrected to obtain the actual amount of fuel to be injected.
In this device, however, since fluctuations in the fuel pressure in the reservoir tank are large, relative to an amount of drop of the fuel pressure in the reservoir tank caused by one fuel injection, the amount by which the fuel pressure in the reservoir tank has dropped can not be precisely detected. Therefore a problem arises in that the actual amount of fuel to be injected can not be precisely determined, and thus the actual amount of fuel to be injected can not be made equal to the calculated target amount of fuel to be injected.